This tutorial describes the basic principles and performance analysis of optical intensity modulators using electrooptic and electroabsorption effects, for use in analog and digital communication systems. These include lithium niobate modulators, semiconductor electroabsorption modulators, semiconductor Mach-Zehnder modulators, and polymer modulators.

Optical intensity modulators for digital and analog applications

A description is given of a GaAs-AlGaAs, loaded-line traveling-wave modulator which has achieved bandwidths up to 36 GHz to date with low ( >

High-speed III-V semiconductor intensity modulators

The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications. >

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

In this paper, the basic principle of operation, design issues, limitations, recent developments and emerging research trends on wide-bandwidth lasers and modulators for radio-frequency photonic applications are reviewed. The topics covered are wide-bandwidth lasers, lumped and traveling-wave electroabsorption modulators, traveling-wave LiNbO/sub 3/, GaAs, and polymer modulators.

Wide-bandwidth lasers and modulators for RF photonics

Active mode locking by monolithic lasers with integrated electroabsorption modulators using strained‐InGaAsP multiple quantum wells is described. The electroabsorption modulator acts as a short optical gate when a sinusoidal voltage is driven at a deep bias point. Pulse widths as short as 2 ps have been obtained at a repetition rate of 16.3 GHz for a 2.5‐mm‐long monolithic laser.

Monolithic strained‐InGaAsP multiple‐quantum‐well lasers with integrated electroabsorption modulators for active mode locking

High-speed modulation over 22 GHz for waveguided InGaAlAs/InAlAs multiple quantum well (MQW) optical modulators is described. A large on/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55- mu m wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure of merit for the MQW modulator are discussed. The frequency response measurements show that the response speed is limited by the RC time constant of the device. This suggests that the speed can be further enhanced by decreasing the size and capacitance of the device. >

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

The modulator has a large on/off ratio, a low driving voltage (4 V), and operates in the 1.55- mu m wavelength region. Small device capacitance (0.2 pF) has been obtained by using spin-coated polyimides under the bonding pads, and small stray capacitance (0.07 pF) and bonding wide inductance (0.3 nH) have been realized. The modulator requires the lowest power yet reported for a high-frequency-operation external modulator. >

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators with bandwidths in excess of 20 GHz at 1.55 mu m

Modulated light spectra were measured in long-wavelength InGaAs-InAlAs multiple-quantum-well intensity modulators under 30-GHz large-signal modulations. The linewidth broadening factor alpha is determined from the relation between the intensity modulation index and the sideband strength relative to the carrier. The minimum alpha value is estimated to be 0.70 at 1.54 mu m, which is almost the same as the lowest value so far reported in a bulk Franz-Keldysh modulator. This is significantly lower than what is obtained from direct-intensity modulation of injection lasers, making this a useful device for application to high-bit-rate long-haul optical communication systems. >

Observation of low-chirp modulation in InGaAs-InAlAs multiple-quantum-well optical modulators under 30 GHz

A high-speed InGaAs/InAlAs multiple-quantum-well (MQW) intensity modulator and an InGaAsP/InGaAs MQW distributed feedback laser were monolithically integrated by using a hybrid growth technique combining molecular beam epitaxy and metalorganic vapor phase epitaxy. An operating drive voltage of only 2.0 V, a 20-dB on/off ratio, and a 3-dB bandwidth greater than 15 GHz were obtained. This device operated stably in a single mode and with a side-mode suppression ratio of more than 50 dB. >

A low-drive-voltage, high-speed monolithic multiple-quantum-well modulator/DFB laser light source

Monolithic integration of an InGaAsP/InGaAs multiple quantum well (MQW) distributed-feedback (DFB) laser with a high-speed InGaAs/InAlAs MQW intensity modulator is demonstrated. A 3-dB bandwidth. in excess of 16 GHz and low-drive-voltage operation (4.0 V) for a 20-dB on-off ratio are obtained. Good coupling efficiency between an MQW DFB laser and an MQW modulator is accomplished using hybrid crystal growth of MO-VPE and MBE. >

H. Asai

Papers

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators with bandwidths in excess of 20 GHz at 1.55 mu m

Observation of low-chirp modulation in InGaAs-InAlAs multiple-quantum-well optical modulators under 30 GHz

A low-drive-voltage, high-speed monolithic multiple-quantum-well modulator/DFB laser light source

High-speed and low-drive-voltage monolithic multiple quantum-well modulator/DFB laser light source